1. Field of the Invention
This invention relates to centrifugal pumps, particularly of the chopper type, and specifically relates to an impeller vane configuration particularly suited for use in a chopper pump.
2. Description of Related Art
Various industries involve or require the processing of solid waste material into a form that can be disposed of in a suitable manner. Certain solid wastes containing or comprising, for example, plastics, metals, animal byproducts and other hard or stringy materials present a particular challenge to processing that material into a disposable form. Therefore, centrifugal pumps of the type known as chopper pumps are typically employed in processing such solid waste material into a reduced size that can be disposed of or processed further as needed.
Impellers used in chopper pumps are characterized by having vanes that are structured with a cutting edge that is positioned to interact with one or more cutting members, generally termed cutter bars or anvils, located at or near the intake of the pump. The interaction of the cutting edge of the impeller vanes and the cutter bar, or anvil, causes cutting and chopping of the solid materials in the influent slurry, thereby reducing the size of the solids. The solids are further directed toward the vanes of the impeller from where the material is expelled out of the pump through a pump outlet.
A minute space exists between the cutting edge of the impeller vanes and the cutter bar which defines the area of interaction where the cutting and chopping of solids occurs. With continued operation of the chopper pump, the solids begin to wear down the cutting edge of the impeller and the minute space between the impeller vanes and the cutter bar widens. Action must then be taken to reduce the space again to improve the cutting action on the solids.
In conventionally known impellers used in chopper pumps, the impeller vanes are configured with a radially extending leading edge that, in radial (i.e., longitudinal) cross section, is curved at its outward extremity. The leading edge of the vane defines the cutting edge of the vane. Examples of such prior art impellers are disclosed in U.S. Pat. No. 4,842,479 to Dorsch and U.S. Pat. No. 5,460,483 to Dorsch. The curvature of the leading edge in such prior art impeller vanes changes as the cutting edge of the impeller vanes wears down. That is, the angle of the cutting edge becomes less aggressive rendering the cutting edge less effective in providing a cutting action on the solids.
Further, prior art impeller vanes have a body portion which is oriented parallel to the rotational axis of the impeller. As such, the vanes are less efficient in directing flow radially outwardly for expulsion of fluid and solids from the pump.
Thus, it would be advantageous in the art to provide a vane configuration for an impeller used in centrifugal pumps, and especially chopper pumps, which is structured with a cutting edge that does not lose its cutting efficacy as the impeller wears down, and one which is configured to improve fluid flow through the impeller.